Origin of the Parallel Roads of Lochaber. 323 



now give this area an excess of water drainage, must in the like 

 manner, during the Glacial period, have there led to an exceptional 

 accumulation of ice. 



With the incoming of this Glacial period, local glaciers must have 

 descended from every mountain range, and so long as the glacier of 

 one steep glen became confluent with another of the same chain flow- 

 ing in the same general direction, so long would their course he 

 uninterrupted, and the propelling and abrading force maintained, as 

 in the Alps at the present day ; but when, emerging from these glens 

 into valleys of small gradients dividing the several mountain chains, 

 they met with glaciers descending from these other ranges, their pro- 

 gress was not only subject to be checked, and their forces neutralized, 

 but their course diverted, for if the lines of natural drainage 

 were barred, the ice took those of least resistance, although such 

 might be up-hill and against the lines of drainage. This, however, 

 could not be effected without excessive pressure and heaping up of 

 the ice at the points of junction. 



These interferences must have been especially frequent in the valley 

 of the Spean. On the one side, the glaciers descending the steep 

 ravines of Larig Leachach, the Cour and others, adjacent on the 

 northern flank of the Ben Nevis range, would issue into Glen Spean 

 and project across it to the Glen Eoy hills opposite. Below to the 

 west, the great Nevis Glen glacier emerged into the valley of the 

 Lochy, while above to the east the great glacier, issuing from Glen 

 Treig, would flow down Glen Spean ; but, meeting with the aforesaid 

 group of glaciers from Ben Nevis, was partly diverted over the flanks 

 of Craig Dhu, and upon the entrance to Glen Boy. 



While the glaciers from this system of mountains were becoming 

 confluent in and filling Glen Spean, those from the opposite range 

 of hills were descending Glen Boy, Glen Feitheil, the Bough Burn, 

 and the other ravines of that chain, and coming into collision with 

 those of the Ben Nevis range. In the same way, the valley of Loch 

 Eil, Glen Nevis, Glen Mhuilinn, Glen Loy, and others were focussing 

 their glaciers upon the end of the Great Glen north of Ben Nevis, 

 barring in that direction the passage of the ice down Glen Spean, 

 and diverting it northward towards Loch Lochy and Loch Oich. 



Therefore, the great mass of ice descending Glen Spean, in con- 

 sequence of meeting with these obstructions, was driven to accumulate 

 in mass in the lower part of that valley opposite Glen Boy, until, 

 overcoming further resistance and confluent with the Ben Nevis mass, 

 it wheeled round into the Great Glen at Loch Lochy, where the united 

 stream found not only a more contracted passage, but, meeting also at 

 right angles the glacier issuing from Glen Arkaig, was forced against 

 and up the entrance to Glen Gluoy opposite. 



The author then points out the many mounds and terraces in the 

 Spean Valley formed of moraine detritus, though since levelled and 

 often masked by a covering of gravel due to subsequent water action. 

 To this cause also he attributes the large accumulation of debris at 

 the entrance to Glen Boy, between Bohuntine and Glen Glaster, 

 where he shows it to be in places 200 or 300 feet deep and to 



